Vehicles used for heavy duty purposes commonly have at the steerable wheels a kingpin assembly mounted at the axle end and carrying the spindle assembly and wheel. A kingbolt, usually in the form of a shaft, simply extends through and is secured in a steering knuckle on one of the axle or spindle assembly and into a yoke on the other thereof. Thrust bearings in the form of washers or roller bearings are interposed between the knuckle and yoke. The sturdy kingpin assembly is commonly mounted at the ends of a solid axle which in turn is commonly "dropped" in the central portion and attached to the vehicle by shackles and leaf springs.
While the kingpin assembly is simple and rugged, the ability to correct camber and/or caster misalignments is limited. Camber is most commonly corrected by bending the axle appropriately with a hydraulic tool which mounts on the axle. Limited caster correction can be gained by shims placed between the axle and leaf springs. If both wheels require equal correction for caster, shims are effective. However, it is often attempted to correct each wheel independently of the other by installing different shims at the springs. This is an illusory solution in that the shim difference merely distorts the springs rather than twisting the robust axle.
In the unique instance of "split kingpin" axles, such as is used in closed knuckle, four wheel drive vehicles, a means is known to correctly align the wheels. U.S Pat. No. 4,795,187 describes a split (or stub) king pin member which is offset but parallel to the original axis of the split king pin. This allows camber correction but is not germane to the single kingpin assembly.